Integrity of aquatic and water-associated systems, D. Impacts of exotic and
invasive species. Much tidal marsh "remediation" in NJ is being done by removing
the invasive reed Phragmites and replacing it with restored Spartina. This is
happening because of the assumption that Phragmites is of low ecological value;
data about the habitat or nutritional values of Phragmites to estuarine systems
are sparse. IF it is useful as food and/or habitat, and (as has been shown elsewhere)
restored Spartina marshes do not reach equivalence with natural marshes for
a decade or more, perhaps these projects should be rethought. It may be more
beneficial to leave the Phragmites in place, and construct more water channels
within the stands to keep the marsh hydrology functioning.

Background

Tidal wetlands are critical for estuarine function, as they are responsible
for a high proportion of estuarine productivity. The marsh grass, Spartina alterniflora
is not generally consumed by aquatic species until it has died and decayed.
Decomposition processes in salt marshes fragment the original dead leaves and
stems into smaller sizes and upgrade the protein content by colonization of
the substrate by bacteria, fungi and protozoa (Odum and de la Cruz, 1967). Deegan
et al. (1990) found that Spartina detritus itself is used by juvenile menhaden,
which have the digestive physiology and morphology to break up cellulose into
usable carbohydrates. Currin et al. (1995) found that the Spartina detritus
was utilized by several consumer species, and noted that the isotopic signature
for standing dead Spartina was different from that of live or senescent plants,
due to aerial decomposition by fungi.

Phragmites australis is an invasive reed that has replaced the native Spartina
alterniflora in many marshes in the Atlantic Coast of the US, particularly in
those considered "disturbed." Phragmites is considered less desirable because
it shades out other species, causes accumulation of sediments and alters patterns
of water flow, reducing habitat heterogeneity and open water space (Buttery
and Lambert, 1965). Although in Europe it is considered a valuable plant (Silberhorn,
1982), in the US it is considered a weedy invader by marsh managers. In recent
years, many expensive efforts at wetland restoration or rehabilitation have
taken place in which elevation and/or drainage patterns have been altered and
Spartina has been replanted, often following Phragmites removal. However, constructed
marshes generally are less productive and diverse than natural marshes. Minello
and Webb (1997) compared natural and created Spartina marshes (up to 15 years
of age) on the Gulf Coast and found benthic infauna density and species richness
were lower in the created marshes. In addition, densities of most fishes and
commercially important crustaceans were lower in the restored marshes. Sacco
et al. (1994) similarly found a decreased faunal community in restored marshes.
Allen et al., (1994) found that mummichogs (Fundulus heteroclitus) in restored
marshes consumed less food than fish inhabiting natural marshes. It may be that
decades, rather than years, are needed before normal marsh functions can be
restored. As has been pointed out by Levin et al. (1996), a process of succession
takes place in created marshes. Therefore, replacing natural with created marshes
will result in an overall loss of productivity.

Despite the general dislike for, and frequent removal of Phragmites in US marsh
management programs, little is known about its contribution to or effects on
estuarine ecology and productivity. There is a general assumption that the plant
has little ecological value. However, Stribling and Cornwell (1997), studying
consumers in a lower salinity wetland, found a greater contribution from C3
plants (e.g. Phragmites) which are present there, in addition to the C4 Spartina
and phytoplankton. This paper thus provides evidence that Phragmites does contribute
in a significant way to the food webs in low salinity areas. Wainright et al.
(1998) come to the same conclusions. Fell et al., 1998 found that Phragmites-dominated
marshes had abundant tidal marsh invertebrates (snails, amphipods, and isopods)
which provided suitable food resources to mummichogs, which moved onto the marshes
and fed on the invertebrates, as they do in Spartina-dominated marshes.

Another important function of wetland plants to estuarine communities is their
role in providing habitat. Salt marshes are well known to be forage habitat
and a predation refuge for larvae and juveniles of estuarine and marine species
(Shenker and Dean, 1979;Weinstein, 1979; Kneib, 1984; McIvor and Odum, 1988).
Some estuarine species, including mummichogs and grass shrimp, utilize the marsh
surface at high tide. The marsh surface functions to provide food for these
animals as well as refuge from predation. Young individuals of both species
may remain on the marsh surface in shallow puddles, even during low tide, an
adaptation to avoid high mortality from larger organisms in subtidal habitats
(Kneib, 1987). While adult mummichogs prey on grass shrimp, larval mummichogs
are preyed on by grass shrimp (Kneib, 1987). Little is known about the impact
of the Phragmites invasion on the habitat functions of tidal marshes to resident
invertebrates and fish.

Fiddler crabs (Uca spp.) are integral components of many marsh systems. Their
burrows serve to aerate the sediments, and are considered beneficial for the
marsh grasses (Montague, 1980). The crabs also benefit from the presence of
the marsh vegetation, which provides cover to hide from predators (Nomann and
Pennings, 1998). Among the shallow habitats utilized during low tide by grass
shrimp and larval mummichogs are fiddler crab burrows (Kneib, 1995).

The degree of use of refuge habitat such as vegetation by potential prey species
can be affected by the presence of predators. Werner et al (1993), using experimental
ponds, found that when predators were absent, juvenile bluegills were found
throughout the pond, but when predators were present, the smaller fish restricted
themselves to the vegetated regions, a safer habitat. Gotceitas et al (1995)
found that juvenile Atlantic cod (Gadus morhua) shifted their habitat from sand
to cobble or kelp when an actively foraging predator was present. Similarly,
juvenile perch (Perca fluviatilis) and roach (Rutilus rutilus) increased the
proportion of time spent in a refuge in the presence of predators (Eklov and
Persson, 1995), and survival increased with increased refuge efficiency (Person
and Eklov, 1995).